the differences in character (charming female/assertive male) are compared with the differences in vocal pitches (and thus, differences in wavelengths).

thus, there's a double meaning to 'different wavelengths', as they literally speak at different wavelengths, and they are metaphorically 'on different wavelengths' as well, or to say, they think differently (a common english idiom)

captain obvious strikes again!_________________Dad said "No! You will BE KILL BY DEMONS"